To be honest, the vocoder mode is the only one that I have any inclination to use. Unless you are doing Andrews Sisters or Mills Bros (and even they don't rigidly block), suspensions, close block chords that clash and resolve against the chord played, passing notes, counter-harmony, those are the things that make great harmony. The slavish blocking around a chord, without those passing notes and resolutions is the hallmark of the artificial harmony generator.

And, I'm afraid, no matter HOW good the actual vocal transposition, immediately SCREAMS 'Machine!'